Tissue treatment system

ABSTRACT

A hair removal device ( 22 ) includes a cooling surface ( 34 ) which is used to contact the skin ( 6 ) prior to exposure to hair tissue-damaging laser light ( 74 ) passing from a radiation source ( 36 ) through a recessed window ( 46 ). The window is laterally offset from the cooling surface and is spaced apart from the cooling surface in a direction away from the patient&#39;s skin to create a gap between the window and the skin. The window preferably includes both an inner window ( 46 ) and an outer, user-replaceable window ( 48 ). The laser-pulse duration is preferably selected according to the general diameter of the hair.

PRIORITY INFORMATION

This application is a continuation of and claims priority from U.S.patent application Ser. No. 10/687,040, filed Oct. 16, 2003 now U.S.Pat. No. 7,041,094, which is a continuation of and claims priority fromU.S. patent application Ser. No. 09/998,821, filed Nov. 15, 2001, nowissued U.S. Pat. No. 6,666,856, which is a divisional of and claimspriority from U.S. patent application Ser. No. 09/270,118, filed Mar.15, 1999, now U.S. Pat. No. 6,383,176, which is related to a ProvisionalPatent Application Ser. No. 60/124,450, and Provisional PatentApplication Ser. No. 60/124,709, both filed on Mar. 15, 1999, thedisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Use of light to denature very specific kinds of tissue has been calledwavelength-selective photo-thermolysis. The use of lasers for thispurpose has been well described in the literature. See, for example, R.G. Wheland, “Laser-assisted hair removal”, Laser in Dermatology, Vol.15, pp. 469-477, and references cited. By choosing a laser with theright wavelength and energy per unit area (fluence), a particularlight-absorbing target substance (chromophore) in living tissue, such asmelanin or hemoglobin, will absorb energy from the laser beam and becomehot enough to destroy functionality in the tissue containing thechromophore. Tissue in the same area that does not have highconcentration of the target chromophore will not be affected.

Hair includes two basic parts, the shaft, which is the portion of thehair above the epidermis, and the root, which is the portion below thesurface of the epidermis. Various tissues surround the root of the hair.Hair color is primarily do to the presence of melanin in the hair.Melanin is created at the base of the hair follicle and is passed intothe hair as it grows. The presence of melanin has made it possible touse lasers and other light sources for hair removal with melanin as thetarget chromophore. The hair follicle and surrounding structure(referred to collectively as hair tissue) are selectively heated whenthe melanin in the hair tissue and in the hair root itself and isexposed to treatment radiation. The hair tissue is thermally damaged sothat a result of the localized heating, many of the exposed hairs lateratrophy and are sloughed from the epidermis.

The early work in this field was centered around a wavelength with veryhigh melanin absorption, the pulsed ruby laser (694 nm). Long pulse rubylasers (as opposed to Q-switched ruby lasers) typically have a pulseduration in the 1 millisecond range. Although the wavelength is highlyabsorbed in melanin, the wavelength selection has significantlimitations with darker skin types as the epidermis can blister from thesuperficial melanin heating.

Many different approaches to hair removal have been explored since theearly ruby laser evaluation. A common trend is a continual shift towardslonger wavelengths, which have less melanin absorption, as it allowstreatment of patients with a darker range of skin tones. Initially,alexandrite (755 nm) was evaluated and later a diode approach (810 nm).The alexandrite laser offers improved clinical capabilities over theruby laser if one considers treatment of darker skin types. However,from engineering and system performance measures, the two systems aresimilar in terms of size, utility requirement, treatment speed, andsystem cost. In contrast, the high pulse energy diode laser allows thesystem to be much smaller than previous systems with an ability to runoff of standard power. One commercially-available system, sold byCoherent of Santa Clara as Lightsheer, weighs in the 45 kg (100 pound)range and allows the physician to treat the darkest skin types withminimal risk of post operative blistering. Unfortunately, the high pulseenergy diode approach is very expensive as it requires up to 100 diodebars to achieve the peak powers needed for the desired clinical result.Another limitation with this approach is in the delivery device. Thecurrent Lightsheer system houses all diodes and associated hardware in ahandpiece that is used in direct contact with the skin. This approachresults in a heavy handpiece, weighing several pounds, that causes userfatigue and an overall bulky design.

Dermatologists have used cooling devices in dermatologic applicationsprior to laser treatment. The purpose is to chill the skin with theunderstanding that exposure to treatment radiation will elevate theepidermal temperature. Chilling lowers the initial temperature so thatthe post treatment temperature at the epidermis will not create aheat-induced blister. U.S. Pat. No. 5,735,844 describes apparatus whichuses a cooled lens, through which radiation passes, pressed against thepatient's skin to cool the epidermis.

SUMMARY OF THE INVENTION

The present invention is directed to a hair removal device and method bywhich hair tissue-damaging radiation passes from a radiation sourcethrough a recessed window to the patient's skin. The hair removal devicealso includes a skin-cooling element having a cooling surface which isused to contact the skin prior to exposure of that skin area to theradiation. The window is laterally offset from the cooling surface aswell as spaced apart from the cooling surface in a direction away fromthe patient's skin so to create a gap between the window and thepatient's skin.

The presence of a gap between the window of the radiation source and thepatient's skin offers several benefits. One problem associated with acontact cooling window in direct contact with the skin is debris buildup. Dermatologic tissue accumulates on the contact window as treatmentpulses are delivered. The window must be periodically wiped in order topreserve the window from local, intense overheating that thermally andmechanically stresses the window and causes pitting. A recessed windowdoes not exhibit this problem. Another advantage is that the window canbe kept warm and above the local dewpoint temperature for both the innerand outer surfaces, so water and other condensables do not collect onit. Since the window is not in contact with the skin, it does not causeany re-heating of the pre-cooled skin.

In one embodiment of a hair removal device the radiation source includesan optical chamber having an exit aperture covered by the recessedwindow and an optical fiber entrance in which an optical fiber can behoused to permit tissue-damaging radiation to pass from the opticalfiber into the optical chamber. The optical chamber may also be heatedto help prevent condensation from forming on the walls of the chamber orthe window. The window may include both an inner window and an outer,user-replaceable window; if the outer window becomes damaged throughuse, it can be easily replaced without affecting the integrity of theoptical chamber. This is an advantage over fixed, single window designsthat are rendered unusable if there is a surface imperfection due to,for example, localized pitting.

The hair removal device may be coupled to a laser which supplies laserlight to the radiation source for passage through the recessed window.The laser may be controlled by user-operated laser power inputsincluding a laser-pulse duration input and one of a laser-pulseamplitude input and a laser-pulse fluence input. The laser-pulseduration input may be adjusted according to the diameter of the hair,which corresponds to the thermal relaxation time of the hair. Therefore,smaller diameter hairs will typically call for shorter laser-pulseduration inputs while larger diameter hairs will call for a longerlaser-pulse duration inputs. Although larger diameter hairs will beselectively heated with short pulses, defined as a pulse durationshorter than the thermal relaxation time of hair, the peak power on theepidermis is unnecessarily higher than it needs to be. This can resultin a heat-induced blister.

Another aspect of the invention relates to a method for removing hairincluding the steps of (1) determining the diameter typical of the hairto be removed, (2) selecting a laser-pulse duration for a hair removaldevice according to this diameter of the hair so that smaller diameterhair results in a shorter laser-pulse duration than larger diameterhair, and (3) applying laser energy through a window of a hair removaldevice of the selected laser-pulse duration to a patient's skin to causethermal injury to hair tissue. This applies to both individual hairs anda plurality of hairs.

The method may include selecting a chosen one of a laser-pulse amplitudeand a laser-pulse fluence prior to the applying step. Further, themethod may also include positioning a cooling element of the hairremoval device against a first target area and then moving, after aperiod of time, the cooling element from the first target area to asecond target area so that the window overlies and is spaced apart fromthe first target area; laser energy is then applied to the first targetarea through the window with the window overlying and spaced apart fromthe first target area.

The pulse duration has been shown to have significant clinicalimplications. A short pulse, typically in the sub-5 ms, range createshigh peak powers because high fluence is required to deliver enoughenergy to achieve the proper clinical endpoint. High peak power tends toheat the epidermis. Longer pulses result in lower peak power.

Shorter wavelengths, such as 694 nm, do not penetrate deeply into thepatient's skin so, some believe, that it may be desirable, with suchshorter wavelengths, to use a convex window pressing against the skin toshorten the path from the window to the hair tissue as is taught by U.S.Pat. No. 5,735,844 patent. It has been found that by the use of longerwavelengths which are still absorbed by melanin, such as 800 to 1200 nm,it is not necessary for the window of the radiation source to pressagainst the patient's skin to effectively irradiate the hair tissue at atarget area.

Another aspect of the invention is the recognition that it is notnecessary to cool the skin the same time it is being irradiated. This isbecause once the skin has been cooled through contact with a coldsurface, removal of the cold surface permits the skin to warm up but itdoes so much more slowly than it has cooled down because it is relyingalmost entirely on convection rather than conduction. Recognizing thefact that the skin remains sufficiently cool for a second or two afterremoval of the cooling surface permits the window of the radiationsource to be positioned spaced apart from the surface of the skin. Thiseliminates some problems created when the window of the radiation sourcedirectly contacts the skin during irradiation, such as window surfacedamage caused by intense heating from hair fragments that are heated bythe laser beam.

A further aspect of the invention is the recognition that radiation inthe longer wavelengths (about 800 to 1200 nm) of the band ofmelanin-absorbing radiation, typically considered from about 600 nm to1200 nm, can be used without the need for the use of chromophorecontaminants as taught by U.S. Pat. No. 5,425,728.

Other features and advantages of the invention will appear from thefollowing description in which the preferred embodiments have been setforth in detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified cross-sectional view of a hair with its rootwithin a hair follicle;

FIG. 2 plots absorption coefficient versus wavelength for differentsubstances including melanin;

FIG. 3 is a schematic representation of a hair removal assembly madeaccording to the invention;

FIG. 3A is a simplified side view of the hair removal device of FIG. 3with portions broken away to show internal detail;

FIG. 3B is a simplified cross-sectional view taken along line 3B-3B ofFIG. 3A;

FIG. 4 is a bottom plan view of the hair removal device of FIG. 3A;

FIG. 4A is an overall view of the lower end of an alternative embodimentof the hair removal device of FIG. 3A;

FIG. 5 is a theoretical plot of fluence versus radial position for adiverging beam;

FIG. 5A shows an idealized plot of how to square off or equalize thefluence of the beam of FIG. 5;

FIG. 6 is a simplified view of the radiation source of FIG. 3 showinghow radiation is reflected from the walls of the reflective chamber tohelp equalize radiation intensity and reduce hot spots;

FIG. 7 shows several idealized plots of temperature versus depth belowthe skin surface;

FIGS. 8A, 8B, 8C and 8D are two isometric views, a top plan view and anend view of another alternative embodiment of the hair removal device ofFIG. 3A with the ergonomically shaped body removed;

FIG. 9 is a simplified partial cross-sectional view of an alternativeembodiment of the hair removal device of FIG. 3A in which the device isconfigured to permit the user to see the skin area being treated; and

FIG. 10 is a simplified view of the bottom of a further alternativeembodiment of the hair removal device of FIG. 3A showing leading andtrailing cooling surfaces.

FIGS. 11A-11K show an embodiment of a power supply for driving a flashlamp herein.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 illustrates, in simplified form, a hair 2 including a shaft 4extending above skin surface 6 and a root 8 extending below the skinsurface. The root 8 passes through epidermis 10 into dermis 12 with thebase of the root being about 4 mm below surface 6. Root 8 is housedwithin hair follicle 14, hair follicle 14 being surrounded by varioustissues including connective tissue sheath 16 and blood vessels 18. Thevarious tissues closely surrounding root 8 and connected with the growthof hair 2, including hair follicle 14 and connective tissue sheath 16,are collectively referred to as hair tissue 20 in this application.

Because melanin is also present in epidermis 10, with darker skin typeshaving more melanin than lighter skin types, it is important that thewavelength be long enough so that absorption is low for the moderateconcentrations in melanin in the epidermis to permit most of the lightto pass through to the root 8 and hair tissue 20 where melaninconcentrations are relatively high compared to the epidermis. Therefore,it is preferred to use wavelengths in the 800 to 1200 nm range; inparticular, an Nd:YAG (neodimium-doped YAG) laser having a wavelength of1.06 micron is preferred because it is a relatively efficient source andthe technology is well developed and readily available.

FIG. 3 illustrates, schematically, a hair removal assembly 21 includinga hand-held hair removal device 22, device 22 shown in more detail inthe simplified views of FIGS. 3A and 3B. Device 22 includes ahand-grippable body 24 having an upper or outer end 26 into which anumbilical cable 28 passes. Body 24 also has a lower or skin contactingend 30 housing a formed aluminum block 32, block 32 having variouscavities to provide various features and functions as described below.Block 32 defines a cooling surface 34, see also FIG. 4, which is used tocontact the patient's skin and cool the skin and prior to irradiation.Surface 34 is a low friction, high lubricity surface to help preventbonding between the cooling surface and the skin.

Aluminum block 32 also houses a radiation source 36. Radiation source 36includes a reflective chamber 38, in this embodiment having a squarecross-sectional shape. Reflective chamber 38 has its walls covered witha highly reflective material, such as gold; the material is chosen forits reflective qualities for the particular wavelength radiation to beused. Other materials, such as dielectric layers combined withhigh-reflectivity metals, could also be used. Chamber 38 has an opticalfiber entrance 40 to permit an optical fiber 42, or a bundle of opticalfibers, to extend into chamber 38. The opposite end of chamber 38 has anexit aperture 44 covered by a recessed window 46. Recessed window 46 isspaced apart from cooling surface 34 by a distance or gap 47, such asabout 1 to 3 mm (0.04 to 0.12 in). Recessed window 46 includes an innerwindow 48, typically permanently or semi-permanently mounted to aluminumblock 32 at exit aperture 44, and an outer window 50. Outer window 50 isremovable secured in place by the use of an clip, not shown, or othersuitable means. Windows 48, 50 are made of a suitable material, such asfused silica, although other materials, such as optical glasses, couldalso be used. By the use of inner and outer windows 48, 50, if outerwindow 50 is damaged, it can be easily replaced by the user.Accordingly, outer window 50 acts as a sacrificial window which ifdamaged, such as can occur through spalling as a result of bits of hairexploding when subjected to high power radiation, can be easilyreplaced.

Cooling surface 34 is cooled through the use of a coolant evaporator 52house within a blind bore 54 formed in aluminum block 30. The coolant,which may be of various commercially available types, commonly Freon® orother fluorinated hydrocarbons, is directed to evaporator 52 through acoolant liquid line 56 and is recycled back to a refrigerant compressor62 through a coolant vapor return line 58. Line 58 coaxially housescoolant liquid line 56, line 58 being housed within thermal insulation60. Lines 56, 58 and insulation 60 pass through umbilical cable 28 torefrigerant compressor 62 associated with a control console 64.Alternatively, cooling surface 34 can be cooled by a thermoelectric,Peltier device instead of the coolant evaporator. This, currentlypreferred, embodiment of the cooling device is discussed below withreference to FIGS. 8A-8D.

While it is desired to cool surface 34, such cooling can result incondensation on the surfaces of radiation source 36, in particular onthe walls of chamber 38 and on recessed window 46. To help prevent this,a separation slot 66 is made between that portion aluminum block 32 usedto cool surface 34 and that portion of the block used for radiationsource 36. An electrical, typically resistive, heating element 68 ispositioned along one wall of slot 66, the right wall as shown in FIGS.3A and 3B, while the other, left wall is covered with thermal insulation70. Heating element 68 is connected to console 64 through a conductor 71extending along umbilical cable 28. In lieu of resistive heating element68, the hot side of a thermoelectric type of heating element, such asdiscussed below with reference to FIGS. 8A-8D, could be used.

Laser hair removal treatments are designed to be effective and yet safe.That is, the treatment should cause thermal damage to hair tissue 20 butnot substantial damage to surrounding tissue, such as blistering to theskin. To do so the energy per unit area (fluence) of the laser beam 74at skin surface 6 must be controlled. Part of this control requires thatthe distance between skin surface 6 and the end of optical fiber 42 becontrolled because beam 74 expands as it passes through reflectivechamber 38. The distribution of energy across the laser beam at the skinsurface should be substantially constant so that no hot spots, whichcould cause local damage to the epidermis, are created. Also, theindividual exposure sites must fit tightly together, commonly called atiled effect, so that there is little or no overlapping of the exposuresites and, at the same time, little or no area is left unexposed. Thesimplest shape that meets this tiling requirement is a rectangle. Othershapes can create a tiled pattern but they have other drawbacks.Reflective chamber 38 and window 46 both have square cross-sectionalshapes for efficient and effective treatment.

FIG. 5 illustrates a graph of fluence versus radial position for adiverging beam, such as from optical fiber 42. What is desired is tosquare off the graph to equalize the fluence over the beam spot. This issuggested in FIG. 5A in which those portions of the beam at the edgesare reflected or folded over back into the main portion of the beam tocreate a generally square wave graph of fluence versus radial position.FIG. 6 illustrates how this is accomplished with the present invention.The walls 72 of chamber 38 are made to be highly reflective of theparticular wavelength of radiation. In the preferred embodiment thewavelength is 1.06 micron and surface 72 is provided with a highlyreflective gold surface. As suggested in FIGS. 5A and 6, the diverginglaser beam 74 not only passes directly through window 46 but the edgeportions of the beam are reflected off the walls 72 back into the mainportion of the beam to create a generally equalized fluence level. Otheroptical arrangements can be used to help equalize the fluence applied toskin surface 6. For example, various devices called optical integratorsor beam homogenizers are well known in the art of laser materialprocessing. The simplicity of the present device is possible because theexit aperture, by virtue of being close to the cooling surface 34, islocated close to the target surface.

In another embodiment, shown in FIG. 9, reflective chamber 38, exitaperture 44 and protective window 46A are spaced much further from theskin surface to, for example, give the practitioner a better view of thetreatment area 73 through a view port 75. View port 75 may be an openregion, as illustrated, or it could include, for example, transparentand/or reflective members to permit direct or indirect viewing of area73. In this case, a lens system 77 is used between exit aperture 44 andwindow 46A to make an image of the exit aperture on the skin surface attreatment area 73. With this approach, the size of the exit apertureneed not be the same size as the treatment area 73 on the skin surface.The size of treatment area 73 could be made variable by proper selectionof the focal length of lens system 77 and the distance between exitaperture 44 and the lens system. This would be useful when it is desiredto use the device for other treatments, such as the treatment ofvaricose veins.

One way to control unwanted thermal damage to the skin is to cool theepidermis. FIG. 7 illustrates several idealized plots of tissuetemperature versus depth below the skin surface. Plot A shows the normalvariation of temperature versus depth with the temperature rapidlyapproaching the normal core temperature of 37° C. Plot B illustrates thetemperature at a range of tissue depth following a laser pulse whenthere has been no prior cooling of the skin. Assuming the energy is highenough to cause thermal damage at a depth of about 2 to 4 mm, thetypical range of depths need to cause damage to hair tissue 20, the skinsurface temperature is hot enough to cause blistering and burning. Theblistering and burning range is indicated by region 76, that is aboveabout 68° C., while the temperature needed to cause hair tissue damageis indicated by region 78, that is above about 48° C. Plot C illustratesthe result of cooling the skin surface after adequate pre-cooling.Adequate pre-cooling has commonly been found to be created when analuminum heat sink, pre-cooled to about 0° C., is applied to the skinsurface for about 1 to 2 seconds. Plot D plots temperature versus skindepth immediately after exposing the skin surface, pre-cooled as in thePlot C, to a laser-pulse similar to that which created Plot B. As can beseen, pre-cooling the skin surface results in prevention of burning orblistering the skin while permitting the target tissue, that is hairtissue 20, to be raised to a sufficiently high temperature to causethermal damage to the tissue. Note that the plots in FIG. 7 are nottaken from actual test data but are idealized plots provided to aidunderstanding the advantages of pre-cooling of the skin.

Several patents discuss surface cooling to prevent tissue damage. See,for example, U.S. Pat. Nos. 5,057,104; 5,282,789 and 5,735,844. Coherentof Santa Clara, Calif. sells a diode laser system for dermatological useas the LightSheer. This product provides a hand piece with a cold windowthrough which the laser exposure occurs. To use the device the window isfirst pressed against the treatment side for a period of time and thenthe laser beam is fired through the window. One of the problems withthis simultaneous cooling technique when applied to laser hair removalis that it takes two to three seconds with the skin in contact with thecooled window to properly cool the skin surface to about 10 to 15° C.Thus, the practitioner must wait for about 2 to 3 seconds at eachtreatment site before firing the laser-pulse.

The present invention eliminates any need to wait prior to firing thelaser-pulse by separating the cooling surface and the laser dischargewindow. As seen in FIG. 4, cooling surface 34 lies adjacent to window 46in the direction of movement indicated by arrow 80. The width of surface34 and window 46 are substantially the same while the length of 34 isabout twice the length of window 46, that is with the length consideredto be in the direction of arrow 80. Assuming a cooling time of 2 secondsis desired, the forward end 82 of cooling surface 34 is placed over thefirst target area on skin surface 6. After about one second in thatposition, device 22 is moved in the direction of arrow 80 the length ofrecessed window 46; in the preferred embodiment this is about onecentimeter. At this time the first target area shifts to a positioncovered by cooling surface 34 but adjacent to window 46. After a secondone-second interval, device 22 is again moved the length of recessedwindow 46; at this time the first target area, which has been cooled fora total of about two seconds, is aligned with recessed window 46. Thepractitioner then presses a fire button 84 on body 24 of device 22causing a laser-pulse to be directed at skin surface 6. The practitionerthen continues moving device 22 and pressing fire button 84 atone-second intervals to provide the desired laser treatment of the skinsurface.

The desired two-second cooling of skin surface 6 could also be done withcooling surface 34 about the same size as window 46. To do so wouldrequire that device 22 be moved only every two seconds, or some otherlength of time needed to cool the skin surface 4. By making coolingsurface 34 with a length greater than the length of window 46, theamount of time between laser-pulses need not be controlled by how longit takes to cool the skin surface. Rather, the device can be designed sothat the time between laser-pulses is chosen to be at a comfortable pacefor the operator while not unduly extending the time the entireprocedure takes. For example, if it is believed that the proper intervalbetween pulses is three-quarters of a second but the skin area needs tobe cooled for three seconds, the length of cooling surface 34 could bemade to be about four times the length of window 46; using theseparameters, moving device 22 by the length of window 46 between eachpulse permits the skin surface to be cooled for the desired threeseconds while the practitioner can operate the fire button at thedesired three-quarter second between pulses. Therefore, the length ofthe cooling surface (Y) is equal to the length of the window (X)multiplied by the time desired to cool the target site (C), the resultdivided by the desired interval between laser pulses (Z); that is,Y=(X×C)/Z. Adjustments to the thermal capacity, thermal conductivity andtemperature of block 30 and cooling surface 32 can also be made to varythe required time needed to cool skin surface 6.

FIG. 4A illustrates an alternative embodiment of the invention in whichwindow 46A is rectangular having a width about three times its length.In this case cooling surface 34A would have a width about equal to thewidth window 46A. However, the length of cooling surface 34A is, like inthe embodiment of FIG. 4, about twice the length of window 46A based onthe premise that the interval between actuation of fire button 84 willbe equal to one-half the length of time it is desired to apply equalsurface 34A to the skin surface to properly cool the skin surface.

The pre-cooling of the skin surface followed by the irradiation is basedon the premise that the skin can be cooled relatively quickly comparedwith the time it takes to warm back to its normal temperature. Forexample, using a cooling surface 34 maintained at about 0° C. andapplying the cooling surface to skin surface 6 for one second lowers theskin surface temperature about 12° C.; application for two secondslowers the skin temperature by about 18° C.; application for threeseconds lowers the skin temperature by about 20° C. Therefore, twoseconds of cooling time appears to be adequate with this particularcooling surface; three seconds of cooling time is better but onlymarginally so. While one second of cooling time does produce asignificant drop in skin temperature, it may not be adequate dependingupon various factors, primarily the amount of pigment in the patient'sskin, the patient's hair color and other such factors. Accordingly, itis believed cooling times from about one to two seconds, and generallymore preferably about two seconds, are expected to produce good resultsat a reasonable pace with the disclosed embodiment.

In another mode of operation which could be used by experiencedpractitioners, the laser system would be set to emit pulses continuouslyat a constant repetition rate of, for example, 1 Hz. The practitionerwould hold the handpiece in continuous contact with the patient's skinand move it at a constant velocity equal to the product of exposure-arealength time repetition rate. This will maximize the rate at which thetreatment proceeds while still providing adequate skin cooling andcomplete coverage.

FIGS. 8A-8D illustrate another alternative embodiment hair removaldevice 22 but with the ergonomically shaped body shown in FIG. 3removed. Device 22A is similar to device 22 but instead of using coolantevaporator 52, device 22 uses a thermoelectric device 88, typically aPeltier device. Thermoelectric device 88 has a warm part and a cold partcreated by the passage of electricity through the thermoelectric device.To remove the heat created, thermoelectric device 88 includes a watercooled heat sink 90 having inlet and outlet lines 92, 94. The cold partof device 88 is thermally coupled to aluminum block 32A so to coolcooling surface 34A.

FIG. 10 illustrates another embodiment of the invention in whichrecessed window 46 is centered between two cooling surfaces 34. Thisprovides two advantages: (1) the practitioner can move device 22 ineither direction, back and forth, without having to rotate thehandpiece, (2) the trailing cooling surface will reduce both pain andtrauma to the skin following the laser exposure. This will beparticularly important for the treatment of patients with darker skintypes.

Another aspect of the invention relates to the control of thelaser-pulse according to the diameter of shaft 4 of hair 2. Part of thisselection is based on the belief that laser-pulse duration should beselected to match the thermal relaxation time of the targeted hair. Forsmall diameter hair the pulse should be shorter while for largerdiameter hair the pulse should be longer. This belief is used inconjunction with the belief that high peak powers should be avoided.Thus, it is preferred to use longer pulse durations with lower peakpowers and to selectively adjust the duration according to the shaftdiameter to minimize or eliminate damage to epidermis 10 while notsacrificing heat transfer to hair tissue 20. With this in mind, it isbelieved that a wavelength in the range of about 800 to 1200 nm would bequite suitable for use with the present invention. For the preferredembodiment a wavelength of 1.06 micron has been chosen. The choice of a1.06 micron laser is beneficial for many reasons. It permits treating ofpatient having darker pigmented skin than the shorter wavelength laserscommonly used. The 1.06 micron laser is relatively efficient, requiresno special cooling and has the ability to create high pulse energy (suchas about 4000 watts in one preferred embodiment) in low duty cyclepulses without large power-consuming support systems. Further the 1.06micron laser can use flash lamp excitation which can be engineered at afraction of the cost of high peak power diode lasers.

FIGS. 11A-11K show a power supply coupled with a flash lamp, and thepower supply features capacitive reservoir energy storage (FIG. 11K)along with the ability to vary the voltage from the rectified line to anupper limit dictated by the voltage rating of the selected component.For efficiency considerations, the power supply includes power factorcorrection to minimize losses and high-line current associated withphase differences. The second stage is a boost regulator. The finalstage is a buck current regulator (FIG. 11F) which enables pulseamplitude and duration control.

Console 64 is provided with control panel 95 (see FIG. 3) having anumber of inputs 96 to provide the desired user control. Inputs 96include a laser-pulse duration input, which is chosen according to thehair shaft diameter. The laser-pulse duration pulse input could beselected in terms of actual or relative time duration or in terms ofactual or relative hair shaft diameter thickness. In addition to thelaser pulse duration (hair shaft diameter) input, control panel 96 alsoincludes one or both of a laser-pulse amplitude input or a laser-pulsefluence input. Other inputs to permit other variables to be controlledcan also be provided. Console 64 may also include a display 98 toprovide the user with information, such as the temperature of coolingsurface 34, optimal laser pulse actuation rate, laser-pulse durationselected, etc. In one preferred embodiment control panel 95 includes thefollowing inputs: keyswitch to start the system and turn it off, standbyand ready buttons to select the state of operation, controls to selectfluence level, pulse width and repetition rate, and emergency-offbutton; and has the option of displaying the following information:laser and handpiece status (ready/not ready), laser emission indicator,and pulse counter.

In use, the operator first determines the general diameter of the hairto be removed from the patient. Then the laser-pulse duration isselected using the appropriate input 96. In one embodiment, typical hairshaft diameters of about 25 to 150 micrometers will result inlaser-pulse durations of about 25 to 150 microseconds. The laser-pulseamplitude or laser-pulse fluence is also selected using an appropriateinput 96. After ensuring that the temperature of cooling surface 34 hasreached the desired operating temperature, the front end 82 of coolingsurface 34 is placed on the initial target area on the patient's skin.To ensure full treatment of the entire area of the skin without missingareas or having excessive overlaps in area, the skin area may betemporarily marked with a set of lines or a grid to help guide device22. Front end 82 of cooling surface 34 is then placed at a first targetarea on the patient's skin. Cooling surface 34 typically remains inplace from about 0.25 to two seconds. In one preferred embodiment,cooling surface 34 remains in place for one second; after the firstsecond, device 22 is moved in the direction of arrow 80 a distance equalto the length of window 46. After remaining at this position for onesecond, the user again moves a distance equal to one window length. Atthis point the first target area has been cooled for the designed twoseconds so the target area can be irradiated by pressing fire button 84during the next one-second interval. Following the firing of a laser andthe expiration of the one-second interval, the operator again movesdevice 22 in the direction arrow 80 one window length and presses firebutton 84 to irradiate skin surface 6 thus causing thermal damage tohair tissue 20. The thermal damage is intended to cause most or all ofthe treated hairs to fall out and preferably not grow back. Thisprocedure continues over the entire treatment area.

Modification and variation can be made to the disclosed embodimentswithout departing from the subject of the invention as defined in thefollowing claims. While the invention has been described primarily withreference to hair-treatment methods, it may also be useful for otherdermatological application.

Any and all patents, patent applications and printed publicationsreferred to above are incorporated by reference.

1. A skin treatment system comprising: a body having a skin-contactingend; the body having a window through which tissue treating radiation istransmitted to an area of skin being treated; a radiation source whichgenerates a pulse of tissue treating radiation that is transmittedthrough the window, and wherein the pulse of tissue treating radiationhas a pulse amplitude and a pulse duration; and a power supply coupledto the radiation source, wherein the power supply includes a buckregulator circuit which controls the pulse amplitude and the pulseduration of the tissue treating radiation; wherein the radiation sourceincludes a flash lamp; wherein the power supply includes a capacitorwhich stores an electrical charge, which is transmitted through theflash lamp and the capacitor is coupled to the flash lamp; and whereinthe buck regulator circuit includes a switch which is coupled with theflash lamp, whereby an amount of electrical charge current transmittedthrough the flash lamp is controlled by an opening and closing of theswitch.
 2. The system of claim 1, further including a skin-coolingelement carried by the body and having a cooling surface at theskin-contacting end.
 3. A skin treatment system comprising: a bodyhaving a skin-contacting end; the body having a window through whichtissue treating radiation is transmitted to an area of skin beingtreated; a radiation source which generates a pulse of tissue treatingradiation that is transmitted through the window, and wherein the pulseof tissue treating radiation has a pulse amplitude and a pulse duration;a power supply coupled to the radiation source wherein the power supplyincludes a buck regulator circuit which controls the pulse amplitude andthe pulse duration of the tissue treating radiation; wherein theradiation source includes a flash lamp; further including a skin-coolingelement carried by the body and having a cooling surface at theskin-contacting end; wherein the power supply includes a capacitor whichstores an electrical charge, which is transmitted through the flash lampand the capacitor is coupled to the flash lamp; and wherein the buckregulator circuit includes a switch which is coupled with the flashlamp, whereby an amount of electrical charge current transmitted throughthe flash lamp is controlled by an opening and closing of the switch. 4.The system of claim 3, wherein the buck regulator circuit furtherincludes an inductor coupled between the flashlamp and the switch. 5.The system of claim 4, further including a current sensor coupledbetween the capacitor and the flash lamp, and control logic whichcontrols opening and closing of the switch based on a signal from thecurrent sensor.
 6. The system of claim 5, wherein the switch is an IGBT.7. A skin treatment system comprising: a body having a skin-contactingend; the body having a window through which tissue treating radiation istransmitted to an area of skin being treated; a radiation source whichgenerates a pulse of tissue treating radiation that is transmittedthrough the window, and wherein the pulse of tissue treating radiationhas a pulse amplitude and a pulse duration; a power supply coupled tothe radiation source, wherein the power supply includes a buck regulatorcircuit which controls the pulse amplitude and the pulse duration of thetissue treating radiation; a skin-cooling element carried by the bodyand having a cooling surface at the skin-contacting end; wherein thewindow is laterally offset from the cooling surface, such that thecooling surface is adjacent to the window and aligned with the windowalong a direction of motion; and wherein the window is spaced apart fromthe cooling surface in a direction away from the patient's skin when thecooling surface is contacting the patient's skin so as to create a gapbetween the window and the patient's skin.
 8. A skin treatment systemcomprising: a body having a skin-contacting end; the body having awindow through which tissue treating radiation is transmitted to an areaof skin being treated; a radiation source which generates a pulse oftissue treating radiation that is transmitted through the window, andwherein the pulse of tissue treating radiation has a pulse amplitude anda pulse duration; a power supply coupled to the radiation source whereinthe power supply includes a buck regulator circuit which controls thepulse amplitude and the pulse duration of the tissue treating radiation;a skin-cooling element carried by the body and having a cooling surfaceat the skin-contacting end; wherein the radiation source includes aflash lamp; wherein the power supply includes a capacitor which storesan electrical charge, which is transmitted through the flash lamp andthe capacitor is coupled to the flash lamp; wherein the buck regulatorcircuit includes a switch and an inductor coupled in series with theflash lamp, whereby an amount of electrical charge current transmittedthrough the flash lamp is controlled by an opening and closing of theswitch; the power supply further comprising including a current sensorwhich senses an amount of electrical current which is transmittedthrough the flashlamp, and the current sensor outputs a signal based onthe sensed amount of electrical current; and wherein the capacitor, thecurrent sensor, the flashlamp, the inductor and switch form anelectrical loop and the switch is opened and closed based at least inpart on the signal from the current sensor.
 9. A skin treatment systemcomprising: a body having a skin-contacting end; the body having awindow through which tissue treating radiation is transmitted to an areaof skin being treated; a radiation source which generates a pulse oftissue treating radiation that is transmitted through the window, andwherein the pulse of tissue treating radiation has a pulse amplitude anda pulse duration; a power supply coupled to the radiation source,wherein the power supply includes a buck regulator circuit whichcontrols the pulse amplitude and the pulse duration of the tissuetreating radiation and wherein said radiation source is flashlampexcited laser.
 10. The system of claim 9, wherein the radiation sourceis a neodymium laser.